1. Field of the Invention
The present invention concerns a method to create an MR angiography image of an examination region and a magnetic resonance system for this. The invention in particular concerns the generation of MR angiography images without use of contrast agent, based on SSFP (Steady State Free Precession) signals.
2. Description of the Prior Art
Contrast agent-enhanced MR angiography is in widespread use due to its high image signal, its short acquisition time and the minimal movement artifacts with simultaneously high spatial resolution. Very fast imaging sequences and an adapted time lapse of the contrast agent bolus with the data acquisition allow the separation of the arterial blood vessels from the venous blood vessels. However, in examination subjects for whom there is a high risk of developing an NSF illness (Nephrogenetic Systemic Fibrosis), contrast agent-enhanced MR angiography should be avoided. Multiple techniques are possible as alternatives: time-of-flight (ToF) angiography is a non-invasive scheme to utilize the effect of incoming, unsaturated spins perpendicularly in the 2D or 3D volume. However, a time-consuming multislice measurement protocol is required for application to peripheral vessels in the legs, for example. Furthermore, phase-sensitive MR angiography methods are known. However, these phase-sensitive methods require an a priori knowledge of the occurring velocity interval of the vessels to be shown. This knowledge is required in order to avoid phase transitions at 0° or 180° (known as phase wrapping).